1. Field of the Invention
This invention relates to a method for the production of inorganic minute globular particles. More particularly, it relates to a method for the production of inorganic minute globular discrete particles, which method enables the particles to be obtained in diameters selected freely on the order of several hundred microns to submicrons (approximately not more than 1 micron) and distributed in a narrow range.
2. Description of the Prior Art
Minute globular particles, owing to the morphological characteristic thereof, manifest a high packing property and a high sliding property, form an optimum raw material for shaped ceramic articles, prove to be useful as coating agent and a high sliding property, form an optimum raw material for shaped ceramic articles, prove to be useful as coating agent and lubricating agent, have a prospect of bringing about an effect of imparting improved properties to powdery materials on being incorporated therein, and promise to gain all the more in importance in the future.
As means for producing globular ceramic particles in a liquid using an inorganic metal salt, a method which obtains globular particles by adding a sol dropwise to a liquid (Japanese Patent Laid-Open SHO No. 57(1982)-84,731) and a method which produces inorganic minute globular particles by means of a liquid-phase intervacial reaction (Japanese Patent Publication SHO No. 57(1982)-55,454), for example, have been known to the art. The specification of Japanese Patent Laid-Open SHO No. 58(1983)-172,233 discloses a method for the production of minute globular particles of a zirconia substance. This method comprises heat-treating minute particles of zirconia substance with a carbonaceous substance interposed therebetween thereby effecting isolation and spheration of the minute particles of the zirconia substance. Japanese Patent Laid-Opens SHO No. 55(1980)-47,137 and SHO No. 55(1980)-132,626 disclose a method for producing globular particles by obtaining a mixed sol from an aqueous solution of a mixture of a zirconium salt with at least one member selected from the group consisting of titanium salts and tin salts, causing the mixed sol to be converted into globular hydrogel particles in a heated medium, allowing the globular hydrogel particles to age, and washing with water and drying the aged globular hydrogel particles. Further, a method (Japanese Patent Laid-Open SHO No. 61(1986)-263,628) which comprises causing an aqueous suspension of fine ceramic powder to be dispersed in the form of small drops in a high boiling liquid thereby forming globular particles and subsequently drying and calcining the globular particles has been known to the art. Further, in the production of globular particles of alumina, a method which effects dropwise addition of alumina sol to oil or organic solvent by the use of a spray nozzle, for example, has been adopted. The particles which are produced by the methods described above have diameters on the order of several microns to some tens of microns. Thus, they do not deserve to be called sufficiently minute.
In the specification of Japanese Patent Laid-Open SHO No. 61(1986)-227,917, there is disclosed a method for the production of minute globular particles of zirconia substance measuring not more than 1 micron (submicron) in diameter by the use of W/O type emulsion which is prepared by mixing an aqueous solution type emulsion which is prepared by mixing an aqueous solution containing a zirconium salt with an organic solvent in the presence of a surfactant.
An object of this invention, therefore, is to provide an improved method for the production of inorganic minute globular particles.
Another object of this invention is to provide a method for the production on a commercial scale of minute globular discrete particles of a composite oxide composed principally of alumina, titania, yttria, tin oxide, or silica in diameters on the order of some hundred microns to submicrons.